Thickness control device for rolling mill

ABSTRACT

An input side thickness of a strip and rolling pressure are continuously measured whereby an output side thickness of the strip is obtained based on the measurements thus obtained. Subsequently, the autocorrelation function and cross-correlation function are obtained according to the thickness both on the input and output sides to obtain a power spectra, after which coherence function is obtained from those spectra thereby determining a contribution factor of the input side thickness to the output side thickness. Thus, when the contribution factor is low, the roll eccentricity is considered to exert a great influence, so that the eccentricity obtained from the aforesaid coherence is fed as a command value in a gagemeter type thickness control system to compensate for the thickness of the strip.

United States Patent Icliiryu et al.

[ June 17, 1975 I1 THICKNESS CONTROL DEVICE FOR ROLLING MILL [75] Inventors: Ken Ichiryu, Mito; Masayuki Shigeta, Katsuta; Toshiyuki Kajiwara, Hitachi, all of Japan [73] Assignee: Hitachi, Ltd., Japan [22] Filed: Aug. 9, 1974 [2]] Appl. No.: 496,209

[30] Foreign Application Priority Data Aug. 22, 1973 Japan 48-93342 521 U.S. Cl 72/8; 72/11 [51] Int. Cl B21b 37/02 [58] Field of Search 72/8, 10, ll, 16, 20, 21

[56] References Cited UNITED STATES PATENTS 3,543,549 12/1970 Howard 72/8 3,580,022 5/1971 Waltz et al 72/8 3,709,009 l/l973 Shiozaki et al. 72/8 Primary Examiner-Milton S. Mehr Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT An input side thickness of a strip and rolling pressure are continuously measured whereby an output side thickness of the strip is obtained based on the measurements thus obtained. Subsequently, the autocorrelation function and cross-correlation function are obtained according to the thickness both on the input and output sides to obtain a power spectra, after which coherence function is obtained from those spectra thereby determining a contribution factor of the input side thickness to the output side thickness. Thus, when the contribution factor is low, the roll eccentricity is considered to exert a great influence, so that the eccentricity obtained from the aforesaid coherence is fed as a command value in a gagemeter type thickness control system to compensate for the thickness of the strip.

4 Claims, 5 Drawing Figures 6 8 ea g/A/ 5 8 PATENTEDJUN 1 7 I975 SHEET FIG.

MJLTIFLIER FIG. 3

PATENTEDJUN I 7 m5 $889504 SHEET x- RAY 3 F I G 2 THICKNESS e THICKNESS GAGE COEFFICIENT DELAY MULTIPLIER CIRCUIT CORRELATOR V|8 CQRRELATDR 49 CORRELATQR V20 (Rm) (Rhl. ['12) m I I I V SPECTRUM v SPE SPECRUM 2| METER 22 g v23 (4 m) (hI,h2) I4 h2) COHERENCE 24 CALCULATOR V ECCENTRICITY 25 CALCULATOR SHEET PATENTEDJUN 17 ms FILTER (IL) COEFFICIENT MULTIPUER FIG. 5

THICKNESS CONTROL DEVICE FOR ROLLING MILL This invention relates to a thickness control device for a rolling mill, and more particularly to a thickness control device of a gagemeter type capable of removing the influence of the roll eccentricity.

Recently, there has been an eager demand for the accuracy of thicknesses of strips, and as a result a gagemeter type automatic thickness control system based on the so'called BISRA-AGC (Automatic gage control developed by BISRA) has made a tremendous progress.

This gagemeter type automatic thickness control system controls values such as a thickness command hd, no-load roll gap S, rolling pressure P, and mill modulus Km so as to satisfy the following equation;

hd- (S P/KM) =0.

Those values are essential for controlling thickness of strips in a rolling mill.

However, the gagemeter type automatic thickness control system has suffered from disadvantages in that the presence of eccentricity in respective rolls leads to the failure to maintain the roll gap constant as well as to meet the objectives of the thickness control. In other words, with the gagemeter type control system, in case the rolling pressure is increased, it is so designed that no-load roll gap S be decreased, assuming that the increase in the rolling pressure has been caused by the increase in thickness of a strip on the input side. However, in case the roll gap is decreased due to roll eccentricity, the rolling pressure will be increased, so that despite a need to increase the roll gap, the aforesaid control system will function so as to decrease the roll gap. Accordingly, it is an important role imposed on the gagemeter type automatic thickness control system to remove or avoid the influence of roll eccentricity.

Meanwhile, many attempts have been made to this problem. However, most of these attempts have failed to meet an intended success, because of too complicated construction or the failure to obtain desired accuracy, with the result of resorting to the skill of operators to solve this problem. For instance, the simplest attempt among the above-referred attempts from viewpoints of control is that a filter which permits passage of only a signal of roll eccentricity cycle fe is incorporated in a feedback loop for the rolling pressure to thereby eliminate this signal from original signals as well as to remove an eccentricity component from a feedback signal, thus presenting an automatic thickness control system. In this attempt, as well, the following disadvantages are encountered:

I. Since input-side thickness variation and roll eccentricity are taken as variation factors of the rolling pressure, the thickness variation component which is arising at the same frequency fe as that or roll eccentricity will be passed therethrough, resulting in excessive thickness variation on input side which should have been corrected essentially.

2. The so-called resonance type filter adapted to tune with a roll eccentricity frequency fe has a given band width (sensitive zone width), thereby presenting shortcoming of passing signals whose frequencies are close to that of the signal intended to be passed therethrough.

Another attempt is that the generating position of roll eccentricity and the frequency thereof are first assumed, and then the thickness is controlled according to the aforesaid assumption. In other words, it is assumed that the roll eccentricity arise at a backup roll, while the frequency of roll eccentricity be fe, and that a roll eccentricity frequency component which has been detected be roll eccentricity alone. In this case, the wave form is Fourier-analyzed to take out the roll eccentricity frequency component alone, thereby compensating for the roll eccentricity component in the thickness control system. 9

However, the disturbance in the roll system occurs in a work roll section, as well, presenting a complicated pattern, including its high frequency component. For this reason, the desired accuracy can not be obtained merely by detecting and compensating for the eccentricity component of a single roll according to the aforesaid system.

It is accordingly an object of the present invention accurately to catch the'fjrjoll eccentricity component, thereby eliminating the-influence of roll eccentricity component on the gagemeter type thickness control system, and to achieve. high accuracy thickness control for a rolling mill. I i

To attain the aforesaid object, the present invention incorporated a principle that input side thickness variation and output side thickness variation are continuously measured, and then the disturbance due to roll eccentricity is determined based on the statistical method according to the correlation function, after which the disturbance thus determined is removed from the thickness control system. More particularly, the autocorrelation functions R111, R112 and crosscorrelation function Rh 1 -h2 for the input side thickness hi and output side thickness k2 are determined and the level of roll eccentricity e is determined according to the coherence function as defined by y (2hlh2)/hl' (iv/22), wherein hl, h2 and hlh2 represent respective power spectra, whereby the value e is fed as a command input to the automatic thickness control system.

In addition, according to the present invention, a filter which is adapted to tune with roll eccentricity frequency is provided in a feedback loop for the rolling pressure thereby to filter the signal. Then, the coefficient ofB= l 'y is multiplied to the signal thus removing the pure roll eccentricity component alone and feeding back only the input side thickness variation component, whereupon the roll eccentricity component obtained in the aforesaid process is reversed of its phase and then fed to the input side more, precisely speaking, compensating phase lag of servo loop of screw down system, to offset the influence thereof.

FIG. 1 is an outline of a gagemeter type automatic thickness control system of a general type, which is used in the present invention;

FIG. 2 is a block diagram for obtaining roll eccentricity according to the gagemeter control method of the present invention;

FIG. 3 is a plot showing coherence obtained in FIG.

FIG. 4 is a block diagram showing the automatic thickness control system ofa gagemeter type according to the present invention; and

FIG. 5 is a block diagram used for obtaining the phase information of the roll based on the rotation pulse of a backup roll.

Referring now to FIG. 1, there is shown a diagram of a gagemeter type automatic thickness control system. As shown in this figure, a rolling mill consists of a work roll 2 adapted directly to roll a strip 1, and a backup roll 3 externally supporting the work roll 2. The roll screw-down operation of the rolling mill is accomplished by means of a hydraulic jack provided at the ends of the lefthand and righthand rolls. The hydraulic jack consists of a hydraulic cylinder 5 and a ram 6 and is so designed as to adjust the roll gap by adjusting the amount of oil within the hydraulic jack with the aid of a servo-valve 4. For the thickness control at the time of rolling, the displacements of the ram 6 is measured by means of a displacement meter 7, and then a measurement thus obtained is fed back to be compared with the thickness command hd. On the other hand, rolling pressure P is measured by a pressure gage 8, and then the measurement value is divided by a mill constant Km at a coefficient multiplier 9 and then the value thus obtained is added to the summing point 10 to be negatively fed back to the thickness command hd. Thus, the aforesaid respective values are controlled so as to meet the relationship, hd (S P/KM) 0, thereby maintaining the thickness of the rolled strip constant.

The fact that the roll eccentricity exerts the important influence on the gagemeter type thickness control system has been referred to under the heading of the description of the prior art.According to the present invention, a statistical technique is used to find roll eccentricity, thereby removing this factor from the thickness control system. Now, the fundamental principle of the present invention will be described hereunder.

In general, the case of the input side thickness of cyclic variation is lesser, and it is considered to be a statistical random signal in its nature. In contrast thereto, the roll eccentricity is a cyclic variation. On the other hand, the output side thickness variation is a function of the input side thickness variation and roll eccentricity variation, and thus it is a random signal. Since the measurable signals, i.e., the input side thickness hl and output side thickness h2 are random signals, respectively, it is necessary to process data as a statistical values in order to obtain roll eccentricity.

As a method for data processing in the present invention, the autocorrelation function and the crosscorrelation function of the input side thickness hl and the output side thickness h2 are first obtained by using a correlator and then the correlation functions are Fourier-integrated to determine the respective power spectra, after which the coherence is calculated therefrom to separate the input side thickness hl and the roll eccentricity e.

The autocorrelation function is defined for the input side thickness hl (t) as follows:

l T T I lim The aforesaid correlation function primarily represents the statistic characteristic of a signal. However, this characteristic will be made further clearer by obtaining power spectrum. This power spectrum corresponds to the square of the Fourier component, which is given as the Fourier transformation of correlation function. Accordingly, the auto power spectra d hl and (bill for the input side thickness hl (t) and output side thickness h2 (I) will be given as follows:

M1 L: Rhle' dr (25/12 L: R1120? d-r while the cross-power spectrum hlh2 for hl (t) and k2 (t) is given as follows:

I Rhined-r As far as the equations (3) and (4) are concerned, e represents a natural logarithmic constant. The autocorrelation function is symmetric with respect to T 0, whereas the cross-correlation function is not symmetric with respect to T: 0. Accordingly, the autopower spectra qbhl and 4 h2 of the input side thickness hl(t) and h2(t) are all real numbers, while the cross power spectrum hlh2 is divided into a real number portion and an imaginary number portion.

The coherence is a factor which represents the relationship of the each input to the output, in case there are multi-input in the control system. Accordingly, by measuring the coherence of input side thickness hl and the output side thickness h2, it can be numerically determined whether the cyclic variation in the output side thickness is stemming from the input side thickness hl or from the roll eccentricity e. This coherence 'y is defined as follows:

: hl.0h2 (5) wherein the product 'y hl of the coherence y and input side thickness [11 represents the contribution of the input side thickness hl to the output side thickness h2. Accordingly, if the roll eccentricity e is zero, 7 1, whereby output side thickness k2 is goverened only by input side thickness hl. Conversely, if 7 l, (l y )hI will be the component of the roll eccentricity e at its frequency. In other words, according to the gagemeter control device of the present invention, the total power in roll eccentricity cycle fe and the power at the pure roll eccentric portion are first determined and then its ratio B l is obtained, after which a roll eccentricity component is fed as an output to the gagemeter type automatic thickness control system, thereby eliminating the influence thereof.

FIG. 2 shows a coherence calculating block serving as a basis for the present invention. The input side thickness hl is measured by means of an X-ray thickness gages 13, 13' for an input side plate 11. The X-ray thickness gage is positioned a distance I ahead of the roll center, so that the input side thickness hl may be obtained at the present time, by providing a delay circuit 14 which is adapted to delay the signal by I /v (v: speed of input side plate). On the other hand, the rolling pressure is measured by means of a load cell 8. This measurement is introduced into a coefficient multiplier 16, and the rolling pressure is multiplied by l/(= KR/ Km: KR gradient of plastic curve of plate to be rolled, Km mill constant), whereby the value of variation in the difference (hl h2) between the input side thickness hi and the output side thickness 122 is obtained. Furthermore, this value is detracted from the input side thickness hl at an summing point 17 thereby to obtain the output side thickness k2. Then, those values hl and I12 are fed as an input to correlators 18, 19 and 20 to obtain autocorrelation functions Rhl and Rh2 and cross-correlation function Rhlh2, which are then Fourier-transformed by means of spectrum meters 21, 22 and 23 to obtain power spectra hl, h2, 41h 1h2. In addition, those values are introduced to a coherence calculator 24 to obtain the coherence defined by 'y ((1)2111 h2)/hl"d h2), obtaining the roll eccentricity component e by means of an eccentricity calculator 25.

As has been described earlier, the coherence represents the relationship of the input side thickness hl to the output side thickness h2. Thus, if the factor affecting the variation in the output side thickness k2 is the input side thickness hl alone, 7 I will be maintained. In contrast thereto, if the factor affecting the output side thickness h2 includes other factors such as roll eccentricity component 6, then 7 1 at the frequency fe. FIG. 3 shows one example. As shown, the coherence function exhibits decrease at several points. This decrease at several points may be attributed to the mixing of the backup roll eccentricity with the work roll eccentricity. Assume that fbl and jb3 are the first and third frequencies of the backup roll, fwl and fw2 are the first and third frequencies of the work roll. The coherence will be lowered from 1, depending on the respective frequencies, suggesting the presence of eccentricity.

The correction of the roll eccentricity component may be determined independently commensurate to the thickness accuracy. In other words, the extent, to which the roll eccentricity affects the output side thickness h2 has been determined as coherence y (f), so that the allowance 7 a of 'y Q) may be set commensurate to the thickness accuracy to be guaranteed. Accordingly, if 7 11 7%,) 1 is met, little influence due to the roll eccentricity will result, presenting sound roll system. According to one example shown in FIG. 3, the third frequency fw3 of the work roll need not be corrected, whilejbl ,fwl and jb3 alone should be corrected.

For correcting operation, it is required to determine the magnitude of the eccentricity (gain) atf=fe, as well as the phase. This phase information may be obtained by setting a reference signal based on the rotation pulse of backup roll or work roll. For instance, if the magnitude of the roll eccentricity in the backup roll system is large at f=fl9l and thus roll eccentricity should be corrected, then its phase may be determined together with the gain, due to the correlation between the rolling pressure and the backup roll rotation. FIG. 5 shows a block until this phase information is fed as an output to the thickness control system. In this figure, the phase information may be obtained by calculating by using a calculator 41 the correlation between the rolling load obtained from a pressure gage 8 and the rotation pulse obtained from a pulse generator 40. Then, the phase information thus obtained is fed as an output from a circuit 42 adapted for compensating the phase delay of the thickness control system.

FIG. 4 shows a block diagram of a typical embodiment of the gagemeter type thickness control system embodying the present invention. In the drawing, shown at G is a transfer function of a positioning servo for the thickness command hd, and the transfer function has a property free of delay and a gain of l in the low frequency zone. On the other hand, or represents a coefficient of the mill modulus control, and in general, a l. The roll eccentricity as disturbance affects the output side thickness hZ, but it is detected as a rolling pressure and is fed to the feedback path 26 through the aforesaid steps. In this respect, the feedback path 26 is divided into a feedback path 27 and a feedback path 28, whereby the signal through the feedback path 27 will be fed to a junction 32, while including the input side thickness component and roll eccentricity component. On the other hand, the signal through the feedback path 28 is passed through a filter 29, whose loss is selectively zero only for the roll eccentricity frequency fe and which is free from a phase delay, and then through the coefficient multiplier 30 of B= l y whereby the roll eccentricity component will be fed as a negative output to the junction 32 from the feedback path 31, only at the roll eccentricity frequency fe.

Therefore, component of input side thickness variation alone is constantly fed negatively at feedback path 33. In addition, the power of roll eccentricity component 2 may be obtained from the block shown in FIG. 2, and the phase may be obtained from the block shown in FIG. 5. Accordingly, if the reverse phase component of a signal (if the transfer function G, delays at frequency fe, some phase compensation is added to e) of this roll eccentricity is added to an summing point 35 from the command path 34, the influence of the roll eccentricity may be automatically offset, thereby constituting a gagemeter type automatic thickness control system.

Meanwhile, if the eccentricity in the work roll system is considerable, the correlation between the rotation pulse of the work roll and the rolling pressure is obtained to determine the roll eccentricity component as has been described earlier, for feeding as an output to the thickness control system as same mentioned earlier.

As is apparent form the foregoing description. according to the present invention, the pure roll eccentricity component alone may be separated, and the roll eccentricity component alone may be completely removed from the gagemeter type automatic control system which is usually used, thereby effecting high accuracy thickness control.

What is claimed is:

I. In a gagemeter type automatic thickness control system in a rolling mill consisting of rolls for rolling a strip, hydraulic jack for imparting a rolling pressure to said rolls, a flow rate control valve for adjusting a roll gap by adjusting the amount of oil in said hydraulic jack, a valve control device, a setting device for feeding a desired thickness command to said control device, and a position detector for detecting the roll gap and feeding back the detected value to said valve control device; a thickness control device, comprising means for detecting an input side thickness and an output side thickness of said strip;

a computing device for obtaining the respective power spectra hl, qShZ, d h3 from the autocorrelation functions Rhl and Rh2 and the crosscorrelation function Rh lh2 and then for obtaining from said power spectra the roll eccentricity based on the coherence defined by (cb hl h2)/h1-h2); and

means for feeding as a command value the roll eccentricity obtained from said computing device, to said plate thickness control device.

2. A thickness control device for a rolling mill as set forth in claim 1, wherein said output thickness detecting means consists of input side thickness detecting means, rolling pressure detecting means and computing measn for calculating an output thickness from said both detecting means.

3. A thickness control device for a rolling mill as set forth in claim 1, wherein said device further comprises:

a filter capable of passing only an output signal tunning with a roll eccentricity frequency, among output signals from said output side thickness detecting means; a co efficient multiplier for taking out a roll eccentricity component along by multiplying the signal passed through said filter by coefficient represented by a function ofB= l 'y means for obtaining a deviation between the output signal passed through said coefficient multiplier and the signal prior to the passage through said filter; and means for feeding as an input said deviation signal to said plate thickness control device as a command value.

4. A thickness control device for a rolling mill as set forth in claim 4, said device further comprises: means for monitoring the decrease of the coherence from 1, continuously; means for determining due to said monitoring if the decrease of coherence falls within allowance; means for computing the eccentricity vector according to the correlation between a reference signal from the rolling mill rotation system and the output side thickness (or rolling pressure); and means for feeding the output signal from said computing device as an input, to said plate thickness control device as a command value.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO, 3,889, 504 Dated June 17, 1975 Inventor(s) Ken Ichiryu, Masayuki Shigeta and Toshiyuki Kajiwara It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7,

line 9, change "qbh3" to -5hlh2-.

Signed and Salad this A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting Ojll'iver Commissioner uflatents and Trademarks 

1. In a gagemeter type automatic thickness control system in a rolling mill consisting of rolls for rolling a strip, hydraulic jack for imparting a rolling pressure to said rolls, a flow rate control valve for adjusting a roll gap by adjusting the amount of oil in said hydraulic jack, a valve control device, a setting device for feeding a desired thickness command to said control device, and a position detector for detecting the roll gap and feeding back the detected value to said valve control device; a thickness control device, comprising means for detecting an input side thickness and an output side thickness of said strip; a computing device for obtaining the respective power spectra phi h1, phi h2, phi h3 from the autocorrelation functions Rh1 and Rh2 and the cross-correlation function Rh1h2 and then for obtaining from said power spectra the roll eccentricity based on the coherence defined by ( phi 2h1 h2)/ phi h1. phi h2); and means for feeding as a command value the roll eccentricity obtained from said computing device, to said plate thickness control device.
 2. A thickness control device for a rolling mill as set forth in claim 1, wherein said output thickness detecting means consists of input side thickness detecting means, rolling pressure detecting means and computing measn for calculating an output thickness from said both detecting means.
 3. A thickness control device for a rolling mill as set forth in claim 1, wherein said device further comprises: a filter capable of passing only an output signal tunning with a roll eccentricity frequency, among output signals from said output side thickness detecting means; a coefficient multiplier for taking out a roll eccentricity component along by multiplying the signal passed through said filter by coefficient represented by a function of Beta 1 - gamma 2; means for obtaining a deviation between the output signal passed through said coefficient multiplier and the signal prior to the passage through said filter; and means for feeding as an input said deviation signal to said plate thickness control device as a command value.
 4. A thickness control device for a rolling mill as set forth in claim 4, said device further comprises: means for monitoring the decrease of the coherence from 1, continuously; means for determining due to said monitoring if the decrease of coherence falls within allowance; means for computing the eccentricity vector according to the correlation between a reference signal from the rolling mill rotation system and the output side thickness (or rolling pressure); and means for feeding the output signal from said computing device as an input, to said plate thickness control device as a command value. 